Conventionally, an oxygen concentration sensor is arranged in an exhaust pipe of an internal combustion engine. An ECU (i.e., electronic control unit) obtains information about an air fuel ratio in an exhaust gas (i.e., exhaust gas air/fuel ratio) based on a signal from the oxygen concentration sensor. These features are disclosed in JP-A-2004-340914 corresponding to US 2005/0000810. A control device for controlling the oxygen concentration sensor detects an element impedance of the oxygen concentration sensor by switching an applied voltage of the sensor from a standard voltage to a sweeping voltage while the ECU obtains the information relating to the exhaust gas air/fuel ratio. In JP-A-2004-340914, a discharging time of the applied voltage of the sensor is determined according to a map data (i.e., a two-dimensional map) of the discharging time, which is made with using a terminal voltage of the sensor before sweeping and a previous detection value of the impedance as variables.
An output signal from the sensor is utilized for an engine control. Accordingly, after the element impedance is detected, it is necessary to recover the applied voltage of the sensor to be the standard voltage. In a conventional method, it is necessary to adapt the map data of the discharging time at each chip set. Therefore, it takes much time to adapt the map data.